Ab8tractThe effects of endogenous factors (plant age, section length, and section location) and environmental factors (temperature and mineral nutrition) upon organ regeneration on isolated root sections of Ohondrilla juncea L. were used to develop a standard assay system for the study of the chemical regulation of regeneration. Bud and root formation and its polarity in the presence of a variety of regulators alone and in combinations were observed quantitatively. Bud numbers were increased by auxin (low concentrations), cytokinin, and gibberellin treatments. High concentra· tions of auxin inhibited bud formation and this effect was reversed by antiauxin, cytokinin, or gibberellin. Adenine did not counteract auxin· induced bud inhibition but adenine and N·6·benzyladenine did counteract inhibition induced by the purine antagonist 2,6·diaminopurine. Numbers of regenerated roots were increased by auxin treatment and reduced by cytokinin and gibberellin treatment. On control and auxin· treated sections, bud formation was strongly polar and proximal and cytokinin and gibberellin treatments lessened the polarity. Growth retardants inhibited regeneration. Of a number of synthetic auxins tested, 2,4.dichlorophenoxy. acet.O.methylhydroxamic acid and 4·amino.3,5,6.trichloropicolinic acid were the most effective inhibitors of bud formation.Mechanisms for the regulation of regeneration are inferred from the results.

No abstract

O. juncea plants were grown in a variety of controlled conditions to determine effects of temperature, photoperiod, and gibberellic acid treatment on stem elongation (bolting) and flowering.

A syslcm was developed for testing the ability of herbicides applied to the shoots of the docp-rootcd weed Chondrilla juiicra to inhibit the regeneration of buds on serial sections along the root. Auxin herbicides known to inhibit regeneration when applied directly to root sections and with a potential for translocaiion or slow metaljolic conversion to an active auxin were selected for testing. The most effective herbicides le.stcd were picloram, jV-(di(;tIiylaminomethyl)-2.4-dichlorophenoxyacct;imide and 2,4diehlorophenoxy-acet-0-melhylhydroxamic acid. Each compound reduced bud loniuitioii along 40 cm of root. The inhibilion of regeneration by the sodium salt of 2.4-D was decreased at temperatures above 25''C. The growth rctar(lant.s rhlornieciual chloride, chlorphonium chloride and B-99ri were tested a. n inhibitors of regenerated-bud growth and rniergenc e when applied to shtxjts; only B-95.' > was inhibitory. Ainitrolc and tris-(laziridinyl) phosphine oxide inhibited bud formation and growth.